LeetCode589. N叉树的前序遍历

题目

法一、递归

 1 class Solution {
 2 public:
 3     vector<int>ans;
 4     void dfs(Node* root){
 5         if(root!=NULL){
 6             ans.push_back(root->val);
 7             for(int i = 0;i < root->children.size();i++)
 8             preorder(root->children[i]);
 9         }
10     }
11     vector<int> preorder(Node* root) {
12         dfs(root);
13         return ans;
14     }
15 };

法二，用栈迭代

 1 class Solution {
 2 public:
 3     vector<int> preorder(Node* root) {
 4       vector<int>ans;
 5       stack<Node*>v;
 6       if(root==NULL) return ans;
 7       v.push(root);
 8       while(!v.empty()){
 9           Node *node = v.top();v.pop();
10           if(node) ans.push_back(node->val);
11           else continue;
12
13           for(int i = node->children.size()-1;i >= 0;i--){
14               v.push(node->children[i]);
15           }
16       }
17       return ans;
18     }
19 };